Vinyl acetate is an important monomer in the production of polyvinyl acetate and polyvinyl alcohol products. Vinyl acetate is conventionally prepared by contacting acetic acid and ethylene with molecular oxygen to form a crude vinyl acetate composition. The reaction is typically conducted in the presence of a suitable catalyst, which may comprise palladium, an alkali metal acetate promoter, and, optionally, a co-promoter, e.g., gold or cadmium, on a catalyst support. U.S. Pat. No. 6,696,596, for example, indicates that it is well known to manufacture vinyl acetate in a reaction in the gas phase with acetic acid and oxygen or oxygen containing gasses over fixed-bed catalysts. U.S. Pat. No. 6,040,474, as another example, describes the manufacture of acetic acid and/or vinyl acetate using two reaction zones wherein the first reaction zone comprises ethylene and/or ethane for oxidation to acetic acid and the second reaction zone comprises acetic acid and ethylene with the product streams being subsequently separated thereby producing vinyl acetate. Also, U.S. Pat. No. 6,476,261, describes an oxidation process for the production of alkenes and carboxylic acids such as ethylene and acetic acid, which are reacted to form vinyl acetate, demonstrating that more than one reaction zone can be used to form the vinyl acetate.
This vinyl acetate reaction, however, lends itself to the production of several by-products including, for example, non-volatile residues such as polymerized vinyl acetate, polymerized ethylene, and heavy ends, such as acetoxyacetic acid and others. Conventionally, the formation of these by-products has been deemed to be detrimental in many respects. For example, the formation of these by-products 1) reduces vinyl acetate yield and 2) may lead to fouling of vinyl acetate production equipment, e.g., purification towers and vaporizers. In conventional processes, a heavy ends tower is utilized to remove these by-products, which are then discarded or incinerated.
In some cases, however, some of these by-products may have value. As such, the formation and improved separation thereof may be beneficial.
Thus, the need exists for improved processes for producing vinyl acetate compositions that 1) yield higher amounts of potentially valuable by-products and/or 2) better facilitate the overall vinyl acetate separation scheme.
The disclosures of all of the references mentioned above are hereby incorporated by reference.